feat: show forked from session id in /status (#9330)

Summary:
- Add forked_from to SessionMeta/SessionConfiguredEvent and persist it
for forked sessions.
- Surface forked_from in /status for tui + tui2 and add snapshots.

codex-rs/exec/tests/event_processor_with_json_output.rs

@@ -75,6 +75,7 @@ fn session_configured_produces_thread_started_event() {
         "e1",
         EventMsg::SessionConfigured(SessionConfiguredEvent {
             session_id,
+            forked_from_id: None,
             model: "codex-mini-latest".to_string(),
             model_provider_id: "test-provider".to_string(),
             approval_policy: AskForApproval::Never,